1. Field of the Invention
This invention relates to sliding bearings that are used for large-sized apparatus such as construction machinery, in which shafts and bearing members are applied with large force of sliding of rocking motion under high surface pressure.
2. Prior Art
The conventional sliding bearing in a relatively large-sized cylindrical shape has been manufactured through powder metallurgy owing to its advantages in production cost and yield. The relatively large-sized sliding bearings used for construction machinery are composed of porous iron sintered alloy of quenched structure containing dispersion of soft copper particles and they are subjected to high surface-pressure with receiving rocking motion at a low speed. (Japanese Laid-Open Patent Publication No. H10-246230). The fine pores of sintered alloy are impregnated with high viscosity lubricating oil, grease or wax or their mixture suitable for the applied surface pressure, or the lubricant is further mixed with a solid lubricant and/or an extreme pressure additive.
As a measure to improve the durability of sliding bearing for construction machinery, it has been proposed that a plurality of parallel rows of ridges of 2 to 12.5 μm in height are formed in the inner circumferential surface along the direction of axis and the area of fine pore openings in the inner surface is reduced by compacting the inner surface portion, thereby improving the durability by supplying sliding portion with lubricant oil with retaining it within the rows of ridges. (Japanese Laid-Open Patent Publication No. 2003-222133). Furthermore, it is proposed that X-shaped oil grooves are formed in the inner surface in order to prevent the bearing surface from abnormal abrasion by facilitating the supply of lubricant to the sliding surface. (Japanese Utility Model Publication No. H8-2494).
The bearing which is composed of a porous iron sintered alloy of quenched structure containing dispersion of soft copper particles and is impregnated with lubricant such as wax, surpasses in wear resistance to a certain extent. However, bearings having more excellent wear resistance are demanded in the field of relevant industry. If oil grooves are formed in inner surface, lubricant oil can be supplied easily to sliding surface to improve the wear resistance, however, when the depth of grooves (height of ridges) is only several micrometers, the rows of ridges are liable to be worn off and the supply of lubricant becomes worse. In the case of the formation of X-shaped grooves, the manufacturing of bearings is somewhat difficult because the grooves must be formed through cutting process.